It is becoming apparent that both in stationary applications, such as wind turbines, and in vehicles, such as hybrid or electric vehicles, electronic systems, which combine new energy storage technologies with electrical drive engineering, will be used more and more in the future. In conventional applications, an electric motor, which is configured, e.g., as a polyphase machine, is controlled by a frequency converter in the form of an inverter. A so-called constant-voltage d.c. link, via which an energy store, generally, a battery, is connected to the d.c. side of the inverter, is characteristic of such systems. In order to be able to satisfy the given power and energy requirements for a specific application, several battery cells are connected in series. Since the current provided by such an energy store must flow through all of the battery cells, and a battery cell can only carry a limited current, battery cells are often additionally connected in parallel in order to increase the maximum current.
In addition to a high overall voltage, the series connection of several battery cells has the problem that the entire energy store fails when a single battery cell fails, since then, battery current may no longer flow. Such a failure of the energy store may lead to a failure of the overall system. In the case of a vehicle, a failure of the drive battery may cause the vehicle to “die.” In other applications, such as the adjustment of the rotor blades of wind turbines, this may even bring about unsafe situations in the event of unfavorable conditions, such as high winds. Therefore, a high degree of reliability of the energy store should always be strived for, “reliability” referring to the ability of a system to operate faultlessly for a predefined period of time.
German Patent Application Nos. DE 10 2010 027857 and DE 10 2010 027861 describe batteries having several battery module lines, which are directly connectible to an electric motor. In this context, the battery module lines have several battery modules connected in series, each battery module having at least one battery cell and an assigned, controllable coupling unit, which allows it, as a function of control signals, to disconnect the specific battery module line or to bypass the at least one respectively assigned battery cell or to switch the at least one respectively assigned battery cell into the respective battery module line. By suitably controlling the coupling units, e.g., with the aid of pulse width modulation, suitable phase signals may be provided for controlling the electric motor, which means that a separate pulse-controlled inverter may be omitted. Consequently, the pulse-controlled inverter necessary for controlling the electric motor is, as it were, integrated into the battery. For the purpose of the present application, these two German applications are incorporated into the present application by reference in their entirety.